Strings and regular expressions

String methods, String.format, StringBuilder, splitting, and regular expressions.

Runs in Zerethon IDE · Java 25 Official Java documentation ↗

Main.java

import java.util.regex.*;

public class Main {
    public static void main(String[] args) {
        String name = "Ada Lovelace";
        System.out.println(name.toUpperCase() + " " + name.length() + " " + name.substring(0, 3) + " " + name.indexOf("Love"));
        System.out.println("  padded  ".strip() + "|" + " " + name.contains("Love") + " " + "ada".equalsIgnoreCase("ADA"));
        System.out.println(String.join("-", "a,b,c".split(",")) + " " + String.format("%.2f|%5d|%03d", 3.14159, 42, 7));

        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < 3; i++) sb.append(i).append(';');
        System.out.println(sb.reverse());

        Matcher m = Pattern.compile("order (\\d+) pending").matcher("Order 12 shipped, order 7 pending");
        System.out.println(m.find() ? m.group(1) : "no match");
        System.out.println("a1b22c".replaceAll("\\d+", "#"));
    }
}

Output

ADA LOVELACE 12 Ada 4
padded| true true
a-b-c 3.14|   42|007
;2;1;0
7
a#b#c

Strings are immutable; building a long string in a loop is faster with StringBuilder.
In a Java string a regex backslash is written twice: "\\d+".
split takes a regex: split on a dot with split("\\.").

Strings and regular expressions

Related topics

Official references